In recent years, a communication system using a femtocell base station has been developed to improve communication quality.
The femtocell base station is a small wireless base station covering a narrow communication area with a radius of about several dozen meters, and installation of the femtocell base station indoors, such as in house or in office, can improve communication quality indoors. Therefore, installation of the femtocell base station allows communication in an area in which an existing macrocell base station cannot communicate. Furthermore, since new installation of a macrocell base station is not necessary, the cost for installing the macrocell base station can be reduced.
Currently, an “existing 3G network”, a communication network for communication through an existing macrocell base station, is used as a communication network (communication system) for connecting a user and a communication provider. If a communication infrastructure different from a communication infrastructure used in an existing 3G network is installed in order to install a femtocell base station, various burdens, such as high cost, are imposed on the user and the communication provider. Therefore, it is preferable to use a communication infrastructure used in an existing 3G network to develop a communication system in which a femtocell base station can be used.
An example of a technique of existing 3G network includes a technique related to 3GPP standardization described in Non-Patent Document 1.
The technique related to 3GPP standardization described in Non-Patent Document 1 illustrates a communication system including WLAN UE and a macrocell base station. However, in Non-Patent Document 1, a communication system installed with a femtocell base station is not considered. Therefore, even if a femtocell base station is used as WLAN UE, communication between the femtocell base station and the UE under control of the femtocell base station cannot be performed using the technique related to 3GPP standardization.
Therefore, in the communication between the femtocell base station and the UE, the secure communication that is ensured in the technique related to 3GPP standardization cannot be ensured.
An example of a related art concerning assurance of the security of communication includes a technique for connecting a non-IMS/MMD-compliant terminal including a SIP function with an IMS/MMD network (see Patent Document 1).
There is also a technique for allowing a public mobile terminal to use both the public mobile communication service and the extension service while protecting a SIP message using IPsec.
Furthermore, there is a technique of 3GPP standardization related to an authentication system of network security (see Non-Patent Document 2).